From the state of the art a range of differently designed automatic lubricating pumps are known which are employed for the lubrication of tools on a construction machine, in particular for hydraulic striking tools such as hydraulic hammers, and are driven automatically, i.e. from the hydraulic circuit on the construction machine without their own power source. The hydraulic circuits for striking tools are characterised in that the hydraulic pressure repeatedly increases; this is achieved by interposing a periodically actuated changeover valve. The change between the rise in pressure and the drop in pressure produces the impact movement of the striking tool. The lubrication of striking tools of this nature, such as described for example in DE-A-34 43 542 or DE-A-198 03 449, is problematical, because, due to the high forces acting on the striking tool and the usually dusty environment, lubricants with a high proportion of solids and a high lubrication pressure must be used.
In DE-A-39 39 785 these problems with the lubrication are solved in that the feed pressure with which the lubricating grease is passed to a lubricating point is normally generated by the high operating pressure of the hydraulic circuit. If the hydraulic pressure is not applied in the operational breaks, the feed piston is moved into an initial position by a return spring. Due to the highly viscous lubricating grease, the returning force of the return spring is not sufficient for the feed piston to automatically draw in lubricating grease. Therefore, the lubricant reservoir has a compression spring in order to move the lubricating grease under pressure to the feed piston and to fill a feed chamber. With the application of the operating pressure the feed piston executes a single feed movement. With a longer operating period, to avoid the feed piston only operating once, a battery operated control device can be provided, which, starting in each case with the initial operation of the striking mechanism, opens a shut-off valve at successive times with a selectable time interval to apply the operating pressure a number of times to the feed piston and to correspondingly execute the feed movement many times.
DE-A-197 04 958 relates to a suction and pump unit which can automatically evacuate the air inclusions even with the use of lubricating grease with a high or very high solids content. To achieve this, the volume swept by a feed piston in operation is divided between a feed section which is connected to the lubricating point by a feed line closed by a non-return valve and a compression section into which a vent line opens. Due to their compressibility, air inclusions in the lubricant lead to the feed piston moving over the feed section without the non-return valve in the feed line opening. When the feed piston sweeps the compression section, the lubricant with the air inclusions is forced through the vent hole. As with the lubricating pump in DE-A-39 39 785, the feed piston in DE-A-197 04 958 also operates with a return spring.
The disadvantage of lubricating pumps as described in DE-A-39 39 785 and DE-A-197 04 958 is that the feed pistons execute one full feed stroke each time the operating pressure is applied. Therefore special measures must be taken to operate the feed piston a number of times during the continuous operation of the striking tool over a longer time period. One such measure is the control device of DE-A-39 39 785 described above. This is however a cost-intensive solution which is prone to faults.
A further measure of ensuring continuous lubrication during the complete operating period of the striking tool is described in DE-U-20 118 920. According to this solution, a progressive metering valve, which periodically extends and withdraws an actuating piston, is included in the bypass line of the hydraulic circuit. A flange shoulder of a freewheeling clutch attached to a shaft is pressed against the actuating piston under the force of a spring. The flange shoulder follows the movement of the actuating piston while the freewheeling clutch prevents reversal of the shaft when the actuating piston is withdrawn. In this way the shaft is moved gradually in a rotational direction and a cam located on the shaft is turned, driving a pump element.
According to the further development of DE-U-202 06 050, the progressive metering valve of DE-U-20 118 920 can be dispensed with if the flange shoulder is directly actuated by the striking mechanism via an actuating arm.
In EP-A-1 112 820 the freewheeling clutch is driven by a weight which moves with the vibrating motion of the striking tool.
In EP-A-1 626 225 a lubricant pump is shown for a vehicle or a constructional, agricultural or industrial machine. The lubricant pump switches automatically from a feed mode, in which the feed piston conveys lubricant to a lubricating point, into a filling mode when a lubricant receptacle is filled under pressure. For the changeover a changeover piston is used on the pressure-fluid side and one is also used on the lubricant side.
With the automatic lubrication device of EP-A-1 643 123 a hydraulic motor is used which drives a reciprocating pump via a cam.
Finally, reference is also made to DE-U-20 2004 008 752, according to which a differential piston arrangement can be used to convert the high hydraulic pressure into a feed pressure, suitable for lubrication.
It can be seen from the state of the art that it has only been possible to obtain an automatic, continuous feed of lubricant during the operation of the striking tool with a high level of constructional complexity. In addition, previous solutions have consumable parts, for example in the form of springs and freewheeling clutches, which can easily fail in continuous operation and limit the service life of the lubricant pump or require short servicing intervals.